Carburetors for supplying mixtures of air and gaseous fuels are known. Their function is to provide throttling means and a responsive metering valve to supply a mixture of suitable richness and quantity to operate the engine at required loads and engine speeds.
This is an old art whose fortunes vary with the relative cost of gasoline and of gaseous fuels such as liquefied petroleum gas or natural gas. They also vary with environmental concerns. For example, even when gaseous fuels cost considerably more than gasoline, their use is still compelled for indoor engine operations. One example is the indoor warehouse forklift where the pollutants from gasoline engines are not tolerated, and the alternatives are battery power or gaseous fuels.
Because of the continuing demand for gaseous fuel carburetors, however variable the demand may be, the art has been crowded with efforts to make a carburetor which is alertly responsive to wide ranges of operating demands and ambient conditions such as atmospheric pressure. Generally the developments have utilized increasingly complicated regulators and metering valves. Their complexity has resulted in higher prices, marginally acceptable exhaust pollution emission, and mechanical performance which degrades with long-continued usage. They also have tended to be quite bulky.
Newer vehicles, especially forklifts, allow very little headroom for the carburetor. Conventional systems inherently have had to be bulky, with a relatively high profile. The carburetor of this invention can supply the demands of a 45 HP engine with a head height of only about three inches. Its other dimensions are similarly minimized. Such small dimensions for its envelope are an important improvement.
Especially for indoor operation, the generation of carbon monoxide is not tolerable. A nearly stoichiometric mixture must be burned efficiently. Slowly degrading performance and frequent adjustments are not considered to be too objectionable in many installations, such as in trucks and automobiles. However, in others they render a carburetor unacceptable. For example, forklift trucks are operated for months at a time without much engine maintenance. This tendency is so pronounced that when forklift carburetors are tested by air quality districts for qualification they must be operated for as long as six months without adjustment, and still perform acceptably. In the course of this extended testing, there is ample opportunity for valves and linkages to wear, and for any latent design defects which would result in improper mixtures to become apparent.
It is another object of this invention to provide valves and linkages which are self-compensating for wear so as to function efficiently without external adjustments for an extended period of time.
Although one might theorize that uniform mixing of a gaseous fuel in an airstream in inherently simple, and is greatly simpler than mixing gasoline into an airstream, this is not the case. Mixing gaseous fuel and vaporizing gasoline involve many of the same problems. One problem arises from the fact that the velocity of the airstream through the carburetor venturi is much faster in the center of the stream than nearer to the wall, where it may be nearly stagnant. Getting the fuel into the total airstream--through the slower and into the faster regions, and mixing well with both, is a considerable problem. The injection of the gaseous fuel into the airstream to produce a uniform mixture has often been attained only at the cost of a longer passage in which to mix the gas and air, resulting in a taller carburetor.
Good mixing is required not only for proper combustion, but also for proper distribution of the charge among the cylinders. When the stream of mixture enters the manifold, it divides to the various cylinders, and if the dividing gases are not uniformly mixed relative to one another, imbalance among the cylinders will result.
It is another object of this invention to provide means for improving the uniformity of mixture in a relatively short path length, thereby enabling a carburetor of lower profile to be made.